1. Field of the Invention
The invention relates to a turbojet engine rotor, on whose circumference are provided oblique recesses for receiving vane roots and which alternate with teeth for separating and retaining the vanes. In the present invention, these teeth have cross-sections, whose shape varies along the rotor axis.
2. Discussion of the Background
In a known design of rotors having vanes for aircraft engines, the recesses are produced by axial or oblique pin settings and have invariable cross-sections over the entire rotor length. This also applies in the case of blade roots, which are slid into the recesses and between the teeth and which serve as supports for the blades.
In the general case where the gas circulation stream surrounding the rotor has a variable internal diameter, the vane roots have portions with a rectangular cross-section, whose height (i.e. extension in the radial direction) linearly varies along the rotor, without their thickness being modified. These portions connect the bulbs of the vane roots, which are located in the recesses, to the blades and contiguous platforms defining the circulation stream and they are referred to as poles.
In order to facilitate the transition of forces essentially due to the centrifugal field from the blade to the pole and then to the vane root, the object of the present invention is to minimize the offsets in the circumferential direction between the blade, the pole and the root, the optimum being to inscribe the section at the base of the blade, i.e. level with the platform, in the section of the pole. This is difficult to achieve due to the blade camber and the blade inclination in the circumferential direction called the setting.
To a certain extent the designer can take account of the blade camber by increasing the pole width, but this is clearly to the detriment of the mass. It is also possible to use oblique and not axial recesses in order to have the direction of the pole and the vane root as close as possible to the direction corresponding to the blade setting.
The use of oblique recesses (10.degree., 15.degree. or more than 20.degree.) as a function of the blade setting is opposed by the increase in the local stresses in the disk teeth and in the recesses, at locations where the direction of the pin settings intersects the ends of the rotor at an acute angle. Thus, in the disk recesses there is an X-shaped stress distribution, which is well known to the experts.
Research has been carried out by the applicant company with a view to lightening the vane roots by giving then variable, thinner shapes, at least outside the recesses, in order to reduce the material volume forming them and thus reduce the stresses in the teeth, but this solution was not adequate, because significant stress concentrations appear on the teeth of the disks due to heterogeneities of forces, particularly of a centrifugal nature, produced by the roots and which were due to variations of the cross-section and weight along the roots.